The invention relates to a keyboard switch for low-profile keyboard equipment, and is a 371 filing of PCT/EP92/02205 filed Sep. 23, 1992.
The industry is making increasing efforts to miniaturize electronic apparatuses for general use. To be emphasized in particular are electronic notebooks, and computers in briefcase size, so-called laptops. With such apparatuses, in particular a low overall height is desirable. For this reason, in particular in the two uses mentioned, the key switches must be made especially flat. Industry therefore demands key switches with low overall height.
For the technical implementation of this demand several possibilities exist. The socalled membrane switch arrays can be made for example particularly flat because the key stroke necessary for contacting is itself only fractions of millimeters.
The small stroke is however a disadvantage with regard to reliability. A further disadvantage of membrane switch arrays is the low flexibility. The key switch arrangement must be defined for each product and cannot be used for other products. This therefore results in increased costs.
For this reason, industry is demanding a keyboard switch which can be used as individual element in a great variety of keyboards and is particularly flat.
This demand is met by a key switch according to DE-OS 3,921,632. In the latter a flexible contact element is pressed against stationary contact elements and thus establishes a conductive connection. The flexible contact element is constructed here as resilient membrane.
Such a key switch is therefore very similar in construction to the known membrane switch arrays. Both types of short stroke elements permit only a small stroke. This is disadvantageous in particular as regards the ergonomics.
In the publication "Ergonomics: Signals and controls", ISO/TC 159/SC4, issued by BSI United Kingdom, it is emphasized inter alia the ideal stroke should be 2-4 mm. Furthermore, ergonomic keyboards should exhibit a special force behaviour, that is they should require a relatively large force at the start of the operation and have a defined switch point in which the contact operation then takes place.
The requirement of a large stroke with defined profile of the operating force is contrary to the requirement of a very flat key switch unless the movement direction for the key switch actuation is mechanically uncoupled from the contact actuation. An example of this can be seen in EP 0 100 936. The key switch movement is converted into a plunger movement and into an operating direction perpendicular thereto. For deflecting the movement, cam surfaces are secured to the plunger and operate a contact perpendicularly to the plunger movement.
It is obvious when constructing a flat key switch to miniaturize the latter in accordance with EP 0 100 936, i.e. to reduce the size of the components by the same scale. This is however not readily possible. For with this particular design the flexible contact or contactor itself acts as resilient element. The spring force consequently changes on miniaturization. This means that, with a true-to-scale miniaturization, higher quality materials must be adopted if any impairment of stability and switching behaviour is to be avoided. This makes the switch element considerably more expensive.
Components which are too small also make assembly difficult so that existing assembly devices cannot readily be employed. Consequently, investments on a relatively large scale are required. The greatest disadvantage for the customer however results from the fact that, with said miniaturization, the quality of the switches cannot be retained if the switch is still to be made economically. This manifests itself above all in the number of operations because the springs break too quickly.
The problem underlying the invention is to provide a flat keyboard switch which permits the greatest possible number of operations with simultaneous flat construction and an ergonomically favorable stroke. In principle, the switch design is however also to be applicable generally to other switches.